This invention relates to a dimensionally stable insulating alkenyl aromatic polymer foam extruded in large cross sections employing specific blowing agents or specific blowing agent mixtures.
One major application for alkenyl aromatic polymer foam, such as styrene polymer foams, is in the field of thermal insulation. Desirably a styrene polymer foam for thermal insulation has an average cell size of less than about 0.3 millimeters and excellent dimensional stability.
One manner in which the thermal insulation value of styrene polymer foams is increased is by the addition of certain fully-halogenated compounds, such as dichlorodifluoromethane, into the styrene polymer foam as a blowing/insulating agent. Such a compound, when contained in the cells of the extruded styrene polymer foam, increases the thermal insulation value.
Another major consideration for extruded styrene polymer foam is dimensional stability. Dimensional stability is particularly important when the extruded styrene polymer foam is employed in construction uses or is laminated to a cementitious layer. For most commercial applications regular rectangular forms are required and while a distorted shape can be cut into a rectangular form, considerable product is lost in cutting and must be discarded as scrap. Another consideration is that if an extruded styrene polymer foam product is not dimensionally stable, then the foamed polystyrene must be maintained in storage for a sufficient length of time until substantially all dimensional instability, such a shrinking, swelling, warping or bulging has stopped.
Still another important consideration is the choice of a blowing/insulating agent. Certain of these agents, particularly fully-halogenated compounds such as dichlorodifluoromethane, when released to the atmosphere upon extrusion of the styrene polymer foam or upon aging of the foam are believed to cause harm to the atmosphere. Thus, it is desirable to reduce or eliminate these fully-halogenated compounds.
Some of these considerations concerning extruded foams and their manufacture are discussed at great length in U.S. Pat. Nos. 2,409,910; 2,515,250; 2,669,751; 2,848,428; 2,928,130; 3,121,130; 3,121,911; 3,770,688; 3,815,674; and 3,960,792, the teachings of which are herein incorporated with reference thereto.
Canadian Patent No. 1,086,450, hereby incorporated by reference, refers to this problem and proposes a variety of low permeability, insulating/blowing agents, or mixtures of those agents, having a permeability through an alkenyl aromatic resinous polymer of not greater than 0.017 times the permeability of nitrogen through the body, a thermal conductivity of less than about 0.10 British Thermal Units-inch per hour per square foot per degree Fahrenheit and having the following formula: EQU R1-CF2-R2
herein R1 is a methyl, ethyl, chloromethyl, dichloromethyl, difluoromethyl, chlorofluoromethyl, fluoromethyl, or trifluoromethyl radical and R2 is hydrogen or a chloro, fluoro, methyl or trifluoromethyl radical with the further characterization that the compound contain no more than 3 carbon atoms and if the compound contains as halogen only 2 fluorine atoms, the compound must have 3 carbons.
1,1,1-trifluoroethane (HFC-143a) is specifically listed in the Canadian patent as being one of a number of low-permeability blowing agents useful in the practice of that invention and 1,1,1,2-tetrafluoroethane (HFC-134a) is contemplated as being within the scope of the formula defining low-permeability blowing agents. Also chlorodifluoromethane (HCFC-22) is listed as a secondary or high-permeability blowing agent useful in the preparation of the foam of the Canadian patent.
However, in Table I of the Canadian patent, it can be seen that polystyrene foam prepared from certain of the low-permeability blowing agents, particularly 1,1-difluoro-1-chloroethane (HCFC-142b), have a dimensional stability which is excessive, although the cell size is 0.20 mm (millimeters) This is particularly noted in Example 16. Examples 14 and 15 of the same Table I appear to solve the dimensional stability problem by using 50/50 and 40/60 (weight of each component by total blowing agent weight) blowing agent mixtures of 1,1-difluoroethane (HFC-152a) and HCFC-142b while retaining a cell sizes of 0.12 mm and 0.14 mm respectively.
U.S. Pat. No. 3,960,792, previously incorporated by reference, teaches how to prepare a dimensionally stable expanded closed cell polystyrene foam body while employing as the fluid foaming agent a volatile material which has a diffusion rate through the polystyrene resin about 0.75 to 6 times the diffusion rate of air through polystyrene resin with the foaming agent being a mixture of at least two compounds having carbon chemically combined therein.
U.S. Pat. No. 4,636,527, hereby incorporated by reference, teaches how to prepare an expanded closed cell polystyrene foam body while employing as the fluid foaming agent a mixture of carbon dioxide and ethyl chloride. Optionally dichlorodifluoromethane, 1,1-difluoro-1-chloroethane and mixtures thereof may also be included as part of the blowing agent mixture.
There is a need to be able to produce a dimensionally stable extruded polystyrene foam body with a non-fully halogenated insulating/blowing agent.
More particularly there is a need to be able to produce a dimensionally stable extruded polystyrene foam body with 1,1,1,2-tetrafluoroethane or 1,1,1-trifluoroethane as the only or major insulating/blowing agent.